This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The goal for this project is to examine if a chemical produced in the body (adenosine) and a receptor found on the cells in the body (P2X receptors) are involved in the reflex that causes a rise in blood pressure and heart rate during exercise in human subjects. If the action of the adenosine (with a drug called aminophylline) is blocked or if the receptor is blocked with Vitamin B6, and the exercise response is reduced, this will show that adenosine or the P2X receptor is involved.